With a beneficial safety profile and quick recovery, minimally invasive glaucoma surgery (MIGS) devices and procedures allow surgeons to intervene early in the treatment of glaucoma to better control pressure with fewer medications. In glaucoma patients undergoing cataract surgery, MIGS procedures are a golden opportunity to lower pressure that should not be squandered.
Here is a review of MIGS procedures and devices along with glaucoma experts’ take on where they fit in the treatment paradigm, patient selection and more.
MIGS and other treatments options
“The array of MIGS devices helps effectively manage glaucoma patients with less invasive measures that can ultimately eliminate or reduce patients’ need for drops,” says Larissa Camejo, MD, CEO and founder at Larissa Camejo, MD Center for Medical and Surgical Eye Care in Jupiter, Fla.
Still, drops are not going anywhere just yet. “Treating with medications does have an advantage of allowing me to get an idea of how aggressive the disease is,” she says
As a first-line treatment, Dr. Camejo often starts with selective laser trabeculoplasty (SLT). This strategy “allows me to get my bearings” and figure out what it will take to control IOP. “Then I can choose what type of surgery — whether it’s MIGS or traditional surgery. The majority of glaucoma specialists take care of advanced cases, so we cannot forget about trabeculectomies and tube shunts, which still have a place. However, by choosing or combining the right MIGS procedures, it is possible to get a similar IOP-lowering effect in some types of patients who will respond amazingly well.”
Inder Paul Singh, MD, also uses SLT first: “Conceptually, it acts as surrogate or a diagnostic tool where the resistance to outflow is.” The LiGHT study showed that patients respond better to SLT the earlier it is used in the disease when there is a healthier overall outflow system, says Dr. Singh, president of The Eye Centers of Racine and Kenosha in Wisconsin. “It works as well as prostaglandins as a first-line treatment with less chance of needing incisional surgery over 4 years. SLT achieves about the same IOPs as medications and eliminates the compliance issue. Plus, SLT patients tend to need less incisional surgery.”
INCREASING TRABECULAR OUTFLOW
Approved by the FDA in 2012, Glaukos’ iStent Trabecular Micro-Bypass Stent is designed to bypass the trabecular meshwork (TM) by connecting Schlemm’s canal with the anterior chamber, resulting in increased outflow and reduced IOP. iStent is delivered via preloaded injector through the phacoemulsification incision, before or after cataract surgery. The 1-mm–long L-shaped device can be used singly or in pairs, as with the newer iStent inject device. This two-in-one design can reduce surgery duration and infection risk, with a safety profile similar to the original.
In one study, the iStent inject achieved an average 2-year IOP reduction of 15% with 1.00 fewer drugs and a 5-year IOP reduction of 18.9% with 0.21 fewer required medications.1 iStent resulted in a 1-year IOP reduction of 9% vs. 4% for phacoemulsification with no MIGS.2 Complications can include transient hyphema and a misplaced or blocked stent.
Ivantis’ Hydrus Microstent is described as an intracanalicular scaffold about 8-mm long. When implanted in Schlemm’s canal, it keeps the channel open and draining. It comes preloaded in an insertion tool and is delivered via the same corneal incision used to extract a cataractous lens. After a cataract procedure with stent implantation, researchers in one study found a 2-year IOP reduction of 12.7% with the Hydrus device and an average medication reduction of 1.5.3
Trabectome and Goniotome
MST’s Trabectome is an electro-cautery and fluidic system that utilizes single-use hand pieces that provide aspiration, irrigation and electrocautery and are designed for partial goniotomy. Trabectome unroofs the TM and inner wall of Schlemm’s canal partially to enable aqueous humor to drain more effectively. The procedure can be performed concurrent with cataract surgery or as a stand-alone procedure in phakics and pseudophakes. While two studies have shown Trabectome’s 2-year IOP reductions at 23% and 44%, these effects are constrained by resistance in Schlemm’s canal and by episcleral venous pressure.4,5
MST’s Goniotome is a disposable single unit version that utilizes the precision blade TM removal and fluidics. It was developed to provide a similar option to Trabectome without the capital expense of the whole equipment system.
Gonioscopy-assisted transluminal trabeculotomy (GATT)
As a form of ab interno trabeculotomy, GATT relies on the gonioscope to guide the creation of an aperture in the TM to admit a microcatheter or suture. Once it has spanned the entire Schlemm’s canal, the microcatheter/suture is withdrawn, leaving a goniotomy in full circumference. GATT is not associated with blebs and does not penetrate the sclera. It has been traditionally used to treat congenital glaucoma in juveniles, but investigations into its use in adults have shown promise.
A recent study of 71 adult eyes treated with GATT showed an average IOP decrease of 4.6 mm Hg at 6 months after surgery.6
Excimer laser trabeculotomy (ELT)
ELT provides a precise means of improving outflow without causing the inflammation and pain associated with a typical response to surgical injury. A gonioscope or endoscope provides immediate locational feedback to aid targeting.
ELT has proven nearly as effective in reducing both IOP and the need for postop medications as more invasive techniques, and it minimizes the sort of tissue trauma that could preclude performing subsequent trabeculotomies, if needed. With a high safety profile and record of long-term efficacy, ELT has the potential to obviate the need for topical glaucoma medications and the potential cost, compliance and side-effect issues.7
Larissa Camejo, MD, uses “creative MIGS combinations,” particularly in younger patients who may need more traditional surgeries in the future or are not good candidates for MIGS. To access the angle, bypass the trabecular meshwork (TM) and enter into the canal of Schlemm, options are iStent or iStent inject (Glaukos) and Hydrus (Ivantis), though these have limitations in accessing the full 360 degrees of the canal. “I most commonly use the OMNI (Sight Sciences) because it has more of a reach and it does not leave an implant behind.” The device can viscodilate up to 360 degrees of the canal, as well as unroof the TM with a goniotomy if the surgeon desires.
“With OMNI, you can tailor how much of the two functions you do, personalizing the procedure; I also sometimes combine it with MicroPulse (Iridex) laser procedure for addressing both inflow and outflow,” Dr. Camejo said. “I have patients well controlled with IOPs of 10 to 12 mm Hg using these techniques. I can also combine MicroPulse with a Baerveldt tube shunt (Johnson & Johnson Vision) that is going to take its time to open. I also combine it with an OMNI so that the patient has some pressure-lowering effect early on. The more the merrier!”
For glaucoma patients with a symptomatic cataract, MIGS has really changed the game, says Arsham Sheybani, MD.
“With so many options now that can reduce the medication burden with a very good safety profile, we rarely do cataract surgery alone — we move to MIGS sooner. There are so many possibilities. For people earlier in the disease course, or for people who are surgery naive, MIGS options should be highly considered.”
Ab interno canaloplasty (ABiC)
A modification to traditional canaloplasty, ABiC does not require a suture to maintain outflow. Rather, it employs a microcatheter with an illuminated tip (iTrack, Ellex) to viscodilate and catheterize the circumference of the TM, Schlemm’s canal and the distal collector channels. No device is implanted, and the eye’s natural drainage system is restored, but the lengthy procedure is surgically challenging and risks damage to Schlemm’s canal and other complications. In a study of 228 eyes, ABiC showed a 1-year mean IOP reduction of 8.1 mm Hg.8
Kahook Dual Blade (KDB)
New World Medical’s KDB is designed to remove TM and the internal wall of Schlemm’s canal without injuring surrounding tissue. The KDB is a one-use knife inserted through a corneal incision. It can be used as a singular procedure or in conjunction with cataract surgery and is incapable of causing thermal injury. In studies, this device has decreased average IOP by 26.4% and medications used by 0.7.9
OMNI Surgical System
The OMNI (Sight Sciences) combines the functions of its two predicate devices — VISCO360 for transluminal viscoelastic delivery and TRAB360 for transluminal goniotomy — in one device. The sequential procedures allow for targeting the three sources of resistance in the conventional outflow pathway (TM/trabeculotomy, Schlemm’s canal/viscodilation and collector channels/viscodilation) with one device through a single clear corneal incision.
A retrospective analysis of 106 eyes of 71 consecutive patients with mild to moderate primary open-angle glaucoma who were treated with the VISCO360 predicate device in combination with cataract surgery showed substantial long-term reductions in both IOP and IOP-lowering medications. At 12 months, investigators reported a 41% IOP reduction (24.6 mm Hg to 14.6 mm Hg) in eyes with a baseline pressure of 18 mm Hg or more (n = 72).10
REDUCING AQUEOUS PRODUCTION
One of the oldest techniques for reducing IOP — destroying the ciliary body — has been a recognized glaucoma treatment for more than 80 years. Accomplished now with a surgical laser probe made by Beaver-Visitec International, damage to the secretory epithelium causes aqueous humor production to decrease. However, because this tissue can regenerate, follow-up treatments may be needed to maintain the effect. In a study of 80 patients, combining cataract extraction with ECP was shown to lower IOP and reduce medications more than extraction alone.11
Patient goals and staging
Inder Paul Singh, MD, notes that the surgeon must clarify the goal of the procedure and understand what is important to the patient. “A patient may have a higher pressure with no medication but be off drops and stable; that is success,” he says.
MIGS allows surgeons a choice of how to get to IOP goals. “To determine which device for what procedure — do I want to bypass the trabecular meshwork or scaffold Schlemm — conceptually I stage resistance,” Dr. Singh says. “Doing so helps me understand what device or procedure to choose based on the mechanism at work. This concept will be more valuable as we develop diagnostic tools to pinpoint resistance to outflow.”
Ultimately, Dr. Singh says MIGS has redefined what he considers controlled glaucoma. “The triad of a stable visual field, optic nerve and IOP is still key. But now, because we have enough data supporting the role noncompliance plays in long-term progression, I consider quality of life and the patient’s ability to comply with drop therapy.”
XEN glaucoma implant
Allergan’s XEN implant, a 6-mm–long collagen-based soft-gel tube, is designed to create filtration outflow from the anterior chamber to the subconjunctival zone while minimizing inflammatory response. It is implanted through a corneal incision, which can be performed during cataract surgery. The XEN device is FDA approved only for cases where a progressive glaucoma patient is unresponsive to drops and initial surgical intervention fails to lower IOP. A study of 41 XENs implanted during cataract surgery revealed a postop mean reduction in IOP of 41.8%, with 2.1 fewer medications and scarce complications.12
Santen’s PreserFlo MicroShunt (formerly InnFocus) is inserted into the anterior chamber to create a bleb in the subconjunctival space. The bleb is treated with mitomycin C to minimize the formation of scars and the chance of the bleb failing. Approved in Europe and in trials in the United States, study results for the new MicroShunt show an average reduction in IOP of 30% to 55%, with significantly reduced need for medications.13
Glaukos’ iStent Supra is designed to reduce IOP by accessing the suprachoroidal space in the eye. It is approximately 4.0 mm in length and curved to follow the eye’s anatomy. iStent Supra is approved for use in Canada and Europe and is undergoing U.S. clinical trials to determine safety and efficacy when combined with cataract surgery.
Solx’s Gold Shunt is a flat stent made of 24-carat gold and is inserted through a scleral incision in any quadrant to connect the anterior chamber with the suprachoroidal space. Designed to treat refractive glaucoma, it is approved in Canada and Europe. Results have been mixed, with one study showing poor performance and others only moderate improvement in IOP.14
After being used in Europe for more than a decade, Alcon’s CyPass Micro-Stent received FDA approval in 2016. In August 2018, the CyPass Micro-Stent was voluntarily withdrawn from the market after 5-year data showed a significant loss of corneal endothelial cell density among CyPass recipients compared with a control group.15
In addition, Arsham Sheybani, MD, assistant professor, Department of Ophthalmology and Visual Science, Washington University School of Medicine, St. Louis, Mo., sees a void in a MIGS option for patients who have failed other procedures, even major glaucoma surgery with multiple devices. “I wish there were a safer alternative to a second or third tube,” Dr. Sheybani says. “There’s no big-gun go-to treatment for those patients, outside of a cyclodestructive procedure. We need a suprachoroidal device for disease that has been surgically managed and is still not under control — something like the Beacon Aqueous Microshunt [formerly the Brown Glaucoma Implant, MicroOptx], which shunts aqueous humor from the anterior chamber to the ocular surface.16 I am excited about new devices in the pipeline for those patients who are running out of surgical options.”
With an array of MIGS options to choose from that boast efficacy and safety, surgeons can approach glaucoma patients with an interventional mindset. Performing a MIGS procedure early in the disease process can stabilize IOP and slow progression. OM
- Arriola-Villalobos P, Martinez-de-la-Casa JM, Diaz-Valle D, et al. Glaukos iStent inject trabecular micro-bypass implantation associated with cataract surgery in patients with coexisting cataract and open-angle glaucoma or ocular hypertension: a long-term study. J Ophthalmol. 2016;2016:1056573.
- Malvankar-Mehta MS, Iordanous Y, Chen YN, et al. iStent with phacoemulsification versus phacoemulsification alone for patients with glaucoma and cataract: a meta-analysis. PLoS One. 2015;10(7):e0131770.
- Pfeiffer N, Garcia-Feijoo J, Martinez-de-la-Casa JM, et al. A randomized trial of a Schlemm’s canal microstent with phacoemulsification for reducing intraocular pressure in open-angle glaucoma. Ophthalmology 2015;122(7):1283-1293.
- Kaplowitz K, Schuman JS, Loewen NA. Techniques and outcomes of minimally-invasive trabecular ablation and bypass surgery. Br J Ophthalmol. 2014;98(5):579-585.
- Minckler D, Baerveldt G, Ramirez MA, et al. Clinical results with the Trabectome, a novel surgical device for treatment of open-angle glaucoma. Trans Am Ophthalmol Soc. 2006;104:40-50.
- Grover DS, Godfrey DG, Smith O, et al. Gonioscopy-assisted transluminal trabeculotomy, ab interno trabeculotomy: technique report and preliminary results. Ophthalmology. 2014;121(4):855-861.
- Berlin MS, Toeteberg-Harms M, Kim E, Giers U. Excimer laser trabeculostomy: an effective microinvasive glaucoma surgery procedure for open-angle glaucoma. American Academy of Ophthalmology website. https://www.aao.org/munnerlyn-laser-surgery-center/excimer-laser-trabeculostomy-effective-microinvasi . Accessed February 5, 2020.
- Korber N. Ab interno canaloplasty for the treatment of glaucoma: a case series study. Spektrum Augenheilkd. 2018;32(6):223-227.
- Greenwood MD, Seibold LK, Radcliffe NM. Goniotomy with a single-use dual blade: short-term results. J Cataract Refract Surg. 2017;43(9):1197-1201.
- Ondrejka S, Körber N. 360° ab-interno Schlemm’s canal viscodilation in primary open-angle glaucoma. Clin Ophthalmol. 2019;13:1235-1246.
- Francis BA, Berke SJ, Dustin L, Noecker R. Endoscopic cyclophotocoagulation combined with phacoemulsification versus phacoemulsification alone in medically controlled glaucoma. J Cataract Refract Surg. 2014;40(8):1313-1321.
- De Gregorio A, Pedrotti E, Russo L, Morselli S. Minimally invasive combined glaucoma and cataract surgery: clinical results of the smallest ab interno gel stent. Int Ophthalmol. 2018;38(3):1129-1134.
- Beckers H. Pinchuk L. Minimally invasive glaucoma surgery with a new ab-externo subconjunctival bypass – current status and review of literature. Eur Ophthalmic Rev. 2019;13(1):27-30.
- Hueber A, Roters S, Jordan JF, Konen W. Retrospective analysis of the success and safety of Gold Micro Shunt Implantation in glaucoma. BMC Ophthalmol. 2013;13:35.
- FDA Safety Communication. Potential eye damage from Alcon Cypass micro-stent used to treat open-angle glaucoma. U.S. Food and Drug Administration website. https://www.fda.gov/medical-devices/safety-communications/potential-eye-damage-alcon-cypass-micro-stent-used-treat-open-angle-glaucoma-fda-safety . Accessed February 5, 2020.
- U.S. National Library of Medicine. Early evaluation of the Brown Glaucoma Implant in patients refractory to drug therapy in the European Union (Early Bird EU). https://clinicaltrials.gov/ct2/show/NCT03634319 . Accessed February 5, 2020.